1. Field of the Invention
The present invention relates to a novel luminescing or light-emitting member that emits visible fluorescence or phosphorescence at room temperature upon the application of an electric field or absorption of excitation energy such as electron rays, X-rays and ultraviolet rays, as well as visible light rays and infrared rays. The present invention also relates to a process for preparing the same and to a novel electroluminescent device that can be applied to a light sources for lighting, display or office automation instruments.
2. Related Background Art
Various types of materials have hitherto been known as luminescing materials capable of emitting visible fluorescence or phosphoresce. For example, "Muki Hikarikagaku", Kagaku Sosetsu No. 39, pp. 210-204, 1983, Japan Chemical Society, discloses that ZnS:Ag/Cl, ZnS:Cu/Al, Y.sub.2 O.sub.2 S:Eu.sup.3+, etc. are usable as a fluorescent substances for use in televisions, and ZnO, etc. when burnt in a reducing atmosphere, may be used a fluorescent substance in fluorescent display tubes.
ZnS fluorescent materials are also used as materials which form a luminescing layer of an electroluminescent device, see Oyo Butsuri, Vol. 51, No. 7, 1982.
Such a luminescing layer is formed as a vapordeposited layer by vapor deposition of ZnS on a substrate, or formed by coating a composition comprising powder of ZnS and an organic binder, which composition is produced by immersing the powder of ZnS in a CuSO.sub.4 solution to lower its resistance, followed by dispersion in the organic binder.
On the other hand, as a material different from the above materials conventionally used, Appl. Phys. Lett. 42(4), 1983 discloses that a film of amorphous silicon (a-Si:H.sub.x) emits visible light at room temperature.
This film is prepared by the HOMOCVD (homogeneous chemical vapor deposition) process using SiH.sub.4 as a raw material. A the film prepared at a film formation substrate temperature of 25.degree. C. has an emission intensity as much as 215 times at room temperature to a GaAs.sub.0.12 P.sub.0.87 :N LED material.
However, the emission intensity of GaAS.sub.0.12 P.sub.0.87 :N in the visible region is originally very small. Therefore, even if the film prepared by HOMOCVD has the emission intensity of 215 times as compared with this, the intensity of the film is too small for practical use.
Moreover, although the HOMOCVD Method, (which is different from conventional CVD) is advantageous in that films can be formed at a film formation substrate temperature of room temperature, SiH.sub.4 gas must still be heated to temperatures as high as 550.degree. C. or more, so that it is disadvantageous in that a large energy is required and that the deposition rate is low.